For some obscure reason, Shell.pm quotes apostrophes (') and backslashes (\) on UNIX, and spaces and quotes (") on Windows. If you set $Shell::raw to true no quoting whatsoever is done, so the only remaining thing to do is to negate the special meaning of characters ',{,},$ inside the awk statement. To be consistent here is an example of what you have to do:

use strict;
use Shell;
my $sh = Shell->new;

$Shell::raw='TRUE';

print $sh->ps("aux | grep firefox | awk \'\{print \$2\}\'");
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